The M2 tide from GEOSAT altimetry

More than 2,000,000 global Geosat altimeter observations taken in 1986-88 have been analyzed for the M2 tide at overlapping points in its Exact Repeat Mission. The results are compatible with Schwiderski's 1980 tide-gage-plus-theory model at a level of 6 cm (rms discrepancy). The gross features of that model (amphidromes and highs) are unchanged. The altimeter solutions are for about 1,000 independent time series, each covering separate 5° by 5° areas of the deep oceans. They have been calibrated through two roughly equal and independent subset analyses employing different arcs of the ERM configuration. Examination of the longest full series (108 records) shows that with further densification in time, significant correction to many other ocean tidal components will be possible.